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Title: Time-of-flight mass measurements for nuclear processes in neutron star crusts

Abstract

The location of electron capture heat sources in the crust of accreting neutron stars depends on the masses of extremely neutron-rich nuclei. We present first results from a new implementation of the time-of-flight technique to measure nuclear masses of rare isotopes at the National Supercon- ducting Cyclotron Laboratory. The masses of 16 neutron-rich nuclei in the Sc Ni element range were determined simultaneously, improving the accuracy compared to previous data in 12 cases. The masses of 61V, 63Cr, 66Mn, and 74Ni were measured for the first time with mass excesses of 30.510(890) MeV, 35.280(650) MeV, 36.900(790) MeV, and 49.210(990) MeV, respectively. With the measurement of the 66Mn mass, the location of the two dominant heat sources in the outer crust of accreting neutron stars, which exhibit so called superbursts, is now experimentally constrained. We find that the location of the 66Fe 66Mn electron capture transition occurs sig- nificantly closer to the surface than previously assumed because our new experimental Q-value is 2.1 MeV smaller than predicted by the FRDM mass model. The results also provide new insights into the structure of neutron-rich nuclei around N = 40.

Authors:
 [1];  [2];  [3];  [1];  [1];  [4];  [1];  [3];  [1];  [1];  [1];  [1];  [5];  [6];  [1];  [7];  [1];  [1];  [1];  [6] more »;  [8];  [3];  [7];  [4] « less
  1. National Superconducting Cyclotron Laboratory (NSCL)
  2. Louisiana State University
  3. Michigan State University, East Lansing
  4. University of Notre Dame, IN
  5. Indian Institute of Technology, Kanpur
  6. ORNL
  7. Los Alamos National Laboratory (LANL)
  8. Ohio State University
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1034370
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 107; Journal Issue: 17
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ACCURACY; ELECTRON CAPTURE; HEAT SOURCES; MASS; MEV RANGE 10-100; NEUTRON STARS; NEUTRON-RICH ISOTOPES; NUCLEI; Q-VALUE; TIME-OF-FLIGHT METHOD

Citation Formats

Estrade, Alfredo, Matos, M., Schatz, Hendrik, Amthor, A. M., Bazin, D., Beard, Mary, Becerril, A., Brown, Edward, Elliot, T, Gade, A., Galaviz, D., George, S., Gupta, Sanjib, Hix, William Raphael, Lau, Rita, Moeller, Peter, Pereira, J., Portillo, M., Rogers, A. M., Shapira, Dan, Smith, E., Stolz, A., Wallace, M., and Wiescher, Michael. Time-of-flight mass measurements for nuclear processes in neutron star crusts. United States: N. p., 2011. Web. doi:10.1103/PhysRevLett.107.172503.
Estrade, Alfredo, Matos, M., Schatz, Hendrik, Amthor, A. M., Bazin, D., Beard, Mary, Becerril, A., Brown, Edward, Elliot, T, Gade, A., Galaviz, D., George, S., Gupta, Sanjib, Hix, William Raphael, Lau, Rita, Moeller, Peter, Pereira, J., Portillo, M., Rogers, A. M., Shapira, Dan, Smith, E., Stolz, A., Wallace, M., & Wiescher, Michael. Time-of-flight mass measurements for nuclear processes in neutron star crusts. United States. doi:10.1103/PhysRevLett.107.172503.
Estrade, Alfredo, Matos, M., Schatz, Hendrik, Amthor, A. M., Bazin, D., Beard, Mary, Becerril, A., Brown, Edward, Elliot, T, Gade, A., Galaviz, D., George, S., Gupta, Sanjib, Hix, William Raphael, Lau, Rita, Moeller, Peter, Pereira, J., Portillo, M., Rogers, A. M., Shapira, Dan, Smith, E., Stolz, A., Wallace, M., and Wiescher, Michael. Sat . "Time-of-flight mass measurements for nuclear processes in neutron star crusts". United States. doi:10.1103/PhysRevLett.107.172503.
@article{osti_1034370,
title = {Time-of-flight mass measurements for nuclear processes in neutron star crusts},
author = {Estrade, Alfredo and Matos, M. and Schatz, Hendrik and Amthor, A. M. and Bazin, D. and Beard, Mary and Becerril, A. and Brown, Edward and Elliot, T and Gade, A. and Galaviz, D. and George, S. and Gupta, Sanjib and Hix, William Raphael and Lau, Rita and Moeller, Peter and Pereira, J. and Portillo, M. and Rogers, A. M. and Shapira, Dan and Smith, E. and Stolz, A. and Wallace, M. and Wiescher, Michael},
abstractNote = {The location of electron capture heat sources in the crust of accreting neutron stars depends on the masses of extremely neutron-rich nuclei. We present first results from a new implementation of the time-of-flight technique to measure nuclear masses of rare isotopes at the National Supercon- ducting Cyclotron Laboratory. The masses of 16 neutron-rich nuclei in the Sc Ni element range were determined simultaneously, improving the accuracy compared to previous data in 12 cases. The masses of 61V, 63Cr, 66Mn, and 74Ni were measured for the first time with mass excesses of 30.510(890) MeV, 35.280(650) MeV, 36.900(790) MeV, and 49.210(990) MeV, respectively. With the measurement of the 66Mn mass, the location of the two dominant heat sources in the outer crust of accreting neutron stars, which exhibit so called superbursts, is now experimentally constrained. We find that the location of the 66Fe 66Mn electron capture transition occurs sig- nificantly closer to the surface than previously assumed because our new experimental Q-value is 2.1 MeV smaller than predicted by the FRDM mass model. The results also provide new insights into the structure of neutron-rich nuclei around N = 40.},
doi = {10.1103/PhysRevLett.107.172503},
journal = {Physical Review Letters},
number = 17,
volume = 107,
place = {United States},
year = {Sat Jan 01 00:00:00 EST 2011},
month = {Sat Jan 01 00:00:00 EST 2011}
}
  • We analyze the effect of neutron superfluidity on the cooling time of inner crust matter in neutron stars, in the case of a rapid cooling of the core. The specific heat of the inner crust, which determines the thermal response of the crust, is calculated in the framework of HFB approach at finite temperature. The calculations are performed with two paring forces chosen to simulate the pairing properties of uniform neutron matter corresponding to the BCS approximation and to many-body techniques including polarization effects. Using a simple model for the heat transport across the inner crust, it is shown thatmore » the two pairing scenarios mentioned above give very different values for the cooling time, i.e., of about 12 and 25 yr.« less
  • Experimental knowledge of nuclear masses of exotic nuclei is important for understanding nu- clear structure far from the valley of -stability, and as a direct input into astrophysical models. Electron capture processes in the crust of accreting neutron stars have been proposed as a heat source that can affect the thermal structure of the star. Nuclear masses of very neutron-rich nu- clides are necessary inputs to model the electron capture process. The time-of-flight (TOF) mass measurement technique allows measurements on very short-lived nuclei. It has been effectively applied using the fast fragment beams produced at the National Superconducting Cyclotron Labmore » (NSCL) to reach masses very far from stability. Measurements were performed for neutron-rich isotopes in the region of the N=32 and N=40 subshells, which coincides with the mass range of carbon superburst ashes. We discuss reaction network calculations performed to investigate the impact of our new measurements and to compare the effect of using different global mass models in the calculations. It is observed that the process is sensitive to the differences in the odd-even mass staggering predicted by the mass models, and our new result for 66Mn has a significant impact on the distribution of heat sources in the crust.« less
  • We review the evolution of the Skyrme-Hartree-Fock-Bogoliubov mass models of the Brussels-Montreal group, with particular emphasis on the steps leading up to the most recent of these models, HFB-17. The extension of these models to the calculation of the equation of state of the inner crust of neutron stars is discussed.
  • We investigate the specific heat of superfluid neutrons in the region of the crust of a neutron star characterized by unusual nuclear shapes, whose possible existence has been recently proposed. To describe pairing properties the results from Reid soft-core potential for nucleon-nucleon interaction are used. It is found that the presence of unusual nuclei causes a sizable increase in the specific heat. The results can have consequences in the study of thermal evolution of young neutron stars.